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PostPosted: Thu Aug 18, 2011 7:13 pm 
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Hi,
I posted this in the wheelbuilding thread but haven't gotten ant responses yet, so I figured I'd also try in the general population.
I have a pair of 36 hole 7800 Dura Ace hubs just lying around, and I thought I'd build up a spare set of race wheels. I wan't to lace them to a pair of Kinlin TB-25's with 24 spokes by skipping every third spoke hole. I'm thinking they will be laced as if they were scalloped hubs like in the photo below.
Does anyone know how to come up with the proper spoke lengths.
Thanks for any help.
Image


Last edited by bricky21 on Fri Aug 19, 2011 6:38 pm, edited 1 time in total.

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PostPosted: Thu Aug 18, 2011 7:20 pm 
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I dont think you can do that on this type of hub. Those flanges will have uneven forces. Some will have two spokes pulling and others will have 1.
Doesnt seem like a good idea.

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PostPosted: Thu Aug 18, 2011 7:41 pm 
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I would lace them just like they are in the photo above.
The notch in those hubs represents the third hole/skipped hole in my hubs.
I'm not seeing how I'd have 2 pulling and one pushing vice versa...what am I missing?


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PostPosted: Thu Aug 18, 2011 7:55 pm 
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You could make a diagram of the position of the spoke holes in a correct 24h hub versus the spoke hole positions of a 36h hub where every 3rd hole is skipped. Correcting for the angle of the spokes arriving at the hub (if they are nearly tangential this might not matter much) you could then estimate the difference in spoke length for your 36h hub versus a correct 24h hub. Will only be a couple of mm at a guess.

That's the empirical way I would do it, others on here will have the maths to provide an answer to numerous decimal places.


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PostPosted: Thu Aug 18, 2011 7:58 pm 
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Worse case scenario I will do that and build with cheap spokes until I figure it out then rebuild with CX-Ray's, but I know there has to be a solution.


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PostPosted: Thu Aug 18, 2011 10:04 pm 
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Image

Image

Image

Image


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PostPosted: Fri Aug 19, 2011 6:32 pm 
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I found an example of a 36 hole hub laced with 24 spokes by Damon Rinard, so it will work, but not quite the way I had envisioned. Regardless I will lace the wheel the same way with the only difference being 2 cross on both sides of the rear wheel(2 cross on the front wheel as well). His calculations show the magic number to be 2.17 cross in order to get the correct spoke length in case anybody is interested.
Image


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PostPosted: Fri Aug 19, 2011 8:13 pm 
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You need to use a stiff rim and one that has center drilled holes for the 24h rear. It is 14 DS, 10 NDS. The 20h front needs to be center drilled also. 20 will work a lot better for the front than 24h.


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Spokes_36-24_14_10.jpg
Spokes_36-24_14_10.jpg [ 6.3 KiB | Viewed 3255 times ]
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Spokes_36hub-20rim.jpg [ 3.38 KiB | Viewed 3255 times ]
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PostPosted: Fri Aug 19, 2011 8:53 pm 
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The calculation is there done for you.

You need to supply rim ERD and hub flange diameter (ie. Spoke-Circle-Diameter on flange) and flange width. Plug into those formulae I have given you for getting the spoke length for a wheel laced in the required fashion. Main point to note in the whole calculation is that it is a 1x lacing.

The above calculation applies for front wheel laced in the fashion described in your original picture. For the rear hub calculation you will need to provide additional data wrt to flange width and flange offset/dishing. But note the 1x lacing considered for the front wheel would no longer apply because one would prefer to use more than just 1x lacing on the rear.
There will be another calculation for the rear once you supply hub data and again lacing pattern.

Having said all this, sounds like an awful waste of a D-Ace hub to build a wheel like this with redundant spoke holes. Look tatty.


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PostPosted: Fri Aug 19, 2011 8:56 pm 
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bricky21 wrote:
I found an example of a 36 hole hub laced with 24 spokes by Damon Rinard, so it will work, but not quite the way I had envisioned. Regardless I will lace the wheel the same way with the only difference being 2 cross on both sides of the rear wheel(2 cross on the front wheel as well). His calculations show the magic number to be 2.17 cross in order to get the correct spoke length in case anybody is interested.


What?? No rim info, nor hub info.


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PostPosted: Fri Aug 19, 2011 9:26 pm 
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bricky21 wrote:
I found an example of a 36 hole hub laced with 24 spokes by Damon Rinard, so it will work, but not quite the way I had envisioned. Regardless I will lace the wheel the same way with the only difference being 2 cross on both sides of the rear wheel(2 cross on the front wheel as well). His calculations show the magic number to be 2.17 cross in order to get the correct spoke length in case anybody is interested.


The reason why he did not use the same cross lacing on the NDS is because it wouldn't line up. You will only get symmetry on one side. The example I gave is symmetrical in the spoking pattern on each side, but 14 DS and 10 NDS.

BTW... calculating lengths is trivial for anyone who passed HS geometry. The tough part is getting symmetrical patterns. On a 36h hub you can do a symmetrical pattern on each side with a 28 or a 20h rim. Of course an 18h rim will work very nicely, since it has half the holes the hub has.


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PostPosted: Fri Aug 19, 2011 10:55 pm 
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rruff wrote:
You need to use a stiff rim and one that has center drilled holes for the 24h rear. It is 14 DS, 10 NDS. The 20h front needs to be center drilled also. 20 will work a lot better for the front than 24h.

Thanks for the drawings those are pretty creative. I have a set of lightly used kinlin XR-270's 20-24 will these be as strong or stronger than TB-25's? Also what spokes would you recommend(175lb.)

cryoplasm wrote:
bricky21 wrote:
I found an example of a 36 hole hub laced with 24 spokes by Damon Rinard, so it will work, but not quite the way I had envisioned. Regardless I will lace the wheel the same way with the only difference being 2 cross on both sides of the rear wheel(2 cross on the front wheel as well). His calculations show the magic number to be 2.17 cross in order to get the correct spoke length in case anybody is interested.


What?? No rim info, nor hub info.


Haven't decided on the rim yet. The way I understood it after reading was that all I needed to do was plug into the spokecalc 2.17 as the cross along with ERD and hub geometry's and I would get the proper spoke length. It doesn't really matter any more though as I will be using the patterns rruff supplied from above. Thanks for the help.


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PostPosted: Fri Aug 19, 2011 11:20 pm 
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bricky21 wrote:
Haven't decided on the rim yet. The way I understood it after reading was that all I needed to do was plug into the spokecalc 2.17 as the cross along with ERD and hub geometry's and I would get the proper spoke length. It doesn't really matter any more though as I will be using the patterns rruff supplied from above. Thanks for the help.


It matters. There are two aspects to lacing. First is the organisation/configuration of the spokes, and the other is the intersections of the spokes in said configuration.

Your original post suggested a front wheel only. There wasn't near enough information for a rear wheel.

Having considered the example given above for the rear wheel. It uses a combination of radial (straigh-pull) spokes and 2x. Surprisingly same patterns applies to both NDS and DS. You will need four different spoke lengths for the rear wheel only. Two different spoke lengths for NDS and two different spoke lengths for DS. They will all still have to be calculated as one length spoke will not fit all positions in the wheel.

Having reviewed the presented example it's a frankly dubious configuration for the rear wheel. There may be unforeseen issues with performance and reliability of the wheel.


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PostPosted: Fri Aug 19, 2011 11:48 pm 
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It appears this whole thing is much more complicated than I originally thought, but thats ok, as I'll no doubt learn a few things along the way. Anyway, I'm looking forward to building these wheels if for nothing else just to see how they perform and what kind of reliability they have.

Best case scenario...they perform well and show reasonable reliability :podium:

Worst case scenario...they totally suck, and I have learned a lesson :scared: .


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PostPosted: Sat Aug 20, 2011 12:55 am 
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Location: Alto, NM
bricky21 wrote:
Thanks for the drawings those are pretty creative. I have a set of lightly used kinlin XR-270's 20-24 will these be as strong or stronger than TB-25's? Also what spokes would you recommend(175lb.)


XR270s should be ok. And any spokes will work.

Like cryoplasm mentioned, you will need multiple spoke lengths, and you need to calculate each from scratch... and then remember where to put each one. However, if you get it built right, it should be a good configuration. Damon Rinard's configuration would certainly be simpler for the rear.


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